Problem: In chemistry class, the girl to boy ratio is $8$ to $4$. If there are a total of $48$ students, how many girls are there?
Explanation: A ratio of $8$ girls to $4$ boys means that a set of $12$ students will have $8$ girls and $4$ boys. A class of $48$ students has $4$ sets of $12$ students. Because we know that there are $8$ girls in each set of $12$ students, the class must have $4$ groups of $8$ girls each. There is a total of $32$ girls in chemistry class.